November 4, 2007
American Society of Nephrology (ASN) Renal Week 2007, San Francisco, CA
Abstract SU-PO279

Activation of Hypoxia Inducible Factors (HIF) Ameliorates Hypoxic Distal Tubular Injury in the Isolated Perfused Rat Kidneys (IPK). Samuel N Heyman ¹, Ahuva Shina¹, Lee A Flippin², Michael Arend², Stephen J Klaus², Seymour Rosen³ and Christian Rosenberger⁴.

1 Hebrew University and Hadassah Hospital, Mt. Scopus, Jerusalem; 2 Fibrogen, Inc.; 3 Beth Israel Deaconess Medical Center and Harvard Medical School, Boston; 4 Charité Virchow, Berlin.

Abstract: Preconditional activation of HIF with specific prolyl-hydroxylase inhibitors (PHI) has been shown to attenuate proximal tubular injury induced by warm ischemia / reperfusion (Bernhardt, JASN 17:1970, 2006). Since distal tubular damage characterizes various forms of hypoxic acute kidney injury (AKI), and as HIF upregulation in these settings occurs predominantly in the renal medulla (Rosenberger, KI 67:531, 2005), we explored the protective effect of the PHI in the IPK, characterized by medullary hypoxic damage. Male SD rats (383±6 grams) were randomly given the PHI FG-4497 (FibroGene®, 50 mg/kg IV) or its vehicle (n=10 per group). Six hours later, the Rt. kidney was perfused for 90 minutes with cell-free Krebs Henselite solution, supplemented with bovine serum albumin, a mixture of 20 amino acids and ³H-inulin, and gassed with 5% CO₂ and 95% O₂. Sequential urine collection and perfusate samples were obtained for functional measurements. At the conclusion of the experiment the kidneys were perfusion-fixed with glutaraldehyde for the morphologic assessment of AKI. The contralateral kidney was used for HIF immunostaining.

As compared with near-negative immunostaining in CTR kidneys, HIF-1 isoforms were markedly upregulated by 6 h at all renal regions in the treatment group. HIF-1alpha was principally found in proximal tubules and medullary CDs, and to a lesser extent in medullary thick limbs (mTALs). HIF-2alpha in the treatment group was expressed in interstitial cells and vascular endothelial cells in the cortex and medulla. FG-4497 treatment resulted in a higher perfusate flow rate (p<0.04, ANOVA), but did not affect urine generation, GFR, TRNa and FEK. Outer medullary hypoxic injury was significantly attenuated in the treatment group: damage was noted in 38.9±7.4% vs. 62.7±4.9% of mTALs in the mid-inner stripe (p<0.02) and in 23.8±6.8% vs. 45.6±7.4% of mTALs the innermost zone of the inner stripe (p<0.05). Tubular injury among S3 segments of proximal tubules in the outer stripe was 8.3±4.1% vs. 16.4±5.4% (NS). These findings illustrate that PHI preconditioning may attenuate hypoxic distal tubular injury in the same fashion it protects proximal tubules. mTAL conservation may be related to the appearance of cellular HIF, as well as to preserved endothelial function and microcirculation.

See also November 7, 2007 press release